as salam alaikum
several ahadith discourage divorce to the point that has been said: "The most hated from what is lawful is divorce". Sometimes divorce is necessary but this usually should take place as a last resort after consulting wise people and attempts of reconciliation. In the case of divorce the husband may accept the separation on his wife's request in return of a payment that she may take or detract from her mahr. This practice is called "khul'ah"
If the situation become islamically unbearable for the wife, she can consult an Islamic Judge that may decide a divorce to take place. Some of the cases that leads an Islamic Judge to such decision are the followings:
1) Refusal of the husband to pay his wife's maintenance.
2) Unacceptable behavior from the husband that unjustifiably hurts and/or abuse his wife physically or emotionally.
3) Lack of religiosity of the husband to the point that becomes unbearable for the wife to continue to live with him.
In any case, it should not be a hasty decision but very pondered one with continuous prayers and appealing to Allah asking for the best outcome.
With prayers for your success.